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$FeCr_{2}O_{4}+Na_{2}CO_{3}+O_{2}\overset{fusion}{\rightarrow}[X]\xrightarrow[H^{+}]{H_{2}O} [Y]\xrightarrow[H^{+}]{H_{2}O}[Z]$

Which of the following statements are true for compounds [X], [Y] and [Z] ?
Option: 1
In all three compounds, the chromium is in +6 oxidation state.

Option: 2
[Z] is a deep-blue violet coloured compound which decomposes rapidly in aqueous solution into Cr⁺³ and dioxygen

Option: 3
Saturated solution of [Y] gives bright orange compound, chromic anhydride, with conc. $H_{2}SO_{4}$

Option: 4
All of the above

Answers (1)

best_answer

Test of Chromium(3+) -

$Cr(OH)_3$ is oxidised to $CrO^{2-}_4$ in presence of $NaOH$ & $H_2O_2$

$2Cr(OH)_3 + H_2O_2 +4OH^{-}\rightarrow 2CrO^{2-}_4 + 8H_2O$

$CrO^{2-}_4$ gives yellow ppt with $Pb^{2+}$

$Pb^{2+} +CrO^{2-}_4 \rightarrow PbCrO_4 Yellow$

$CrO^{2-}_4$ in acidic medium with $H_2O_2 \: gives\: CrO_5 \: (Blue)$

$CrO^{2-}_4 +2H^{+} + 2H_2O_2 \rightarrow CrO_5(Blue) +3H_2O_2 \:$

- wherein

Yellow $PbCrO_4 \: and \: blue \: CrO_3\:confirmed \:the \:presence \:of\:Cr^{3+}$

$4FeCr_{2}O_{4}+8Na_{2}CO_{3}+7O_{2}\overset{fusion}{\rightarrow}Na_{2}CrO_{4}\xrightarrow[H^{+}]{H_{2}O} Na_{2}Cr_{2}O_{7}\xrightarrow[H^{+}]{H_{2}O}CrO(O_{2})_2$

deep blue violet $\overset{H_{2}O}{\rightarrow}O_{2}+H_{2}O+Cr^{+3}$

$Na_{2}Cr_{2}O_{7}+H_{2}SO_{4}\rightarrow 2CrO_{3}$ (chromic anhydride) $+Na_{2}SO_{4}+H_{2}O$

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